Door closure apparatus are in general use in commercial locations throughout the country and have been patented for decades. Unfortunately, the earlier devices disclosed here are often incompatible with ADA requirements.
Door closers and shock absorbers are known in the marketplace and are disclosed in several existing patents. By way of example, Scheck, Storandt and Feucht patented a door closure in 1988, U.S. Pat. No. 4,744,125 for a “Door Closer Transmission Including An Eccentric Pinion” that purports to disclose a device having a housing containing an outer piston and an inner piston, each piston being biased by its own compression spring that compresses with the opening of a door to which the door closer is attached. The outer piston includes a rack that engages a gear mounted to an axle that rotates upon door opening. The inner piston includes an abutment that is engaged by a rotating element also connected to the door-opening axle. Because of different geometries of the rack and the rotating element, the compression of the outer piston spring is linear as a function of the door-opening angle. The inner piston spring has a greater return force at small door angles but less force as the angle of opening increases. In 1998 U.S. Pat. No. 5,850,671 for a “Door Closer” issued to Kaser and purports to disclose an apparatus having a housing filled with hydraulic fluid, a main piston, an auxiliary piston, a rack, a closer shaft with a pinion, two strong compression springs, one weaker compression spring and various fluid passages and valves. When an attached door is opened the pinion and rack move the main piston to compress the strong compression springs and fluid is transferred. The weak spring remains in a compressed condition between the auxiliary piston and the main piston. After the door is opened and the opening force is released, the door quickly closes under the strong biasing force of the two strong compression springs during a first time phase. During a next second phase, the door closes more slowly because fluid is restricted through an overflow duct so that movement of the pistons is due to the weaker compression spring. If the door does close completely during the second phase, fluid again flows more freely and all three springs bias the door closed.
U.S. Pat. No. 4,928,799 for a “Hydraulic Dashpot” issued in 1990 to Zachiesche and purports to disclose a dashpot with an automatic closure when a valve located between the dashpot and a hydraulic storage chamber is removed for inspection. The dashpot includes the usual cylindrical housing, a piston, first and second hydraulic chambers one to each side of the piston, a piston rod and oppositely placed connecting elements, one connected to the housing and the other to the rod. In communication with the hydraulic chambers are the pressurized hydraulic storage chamber, a feed line and two valves. In 1991 U.S. Pat. No. 5,018,607 issued for a “Hydraulic Dashpot For Pipeline Systems” to Hardtke and Bernert and purports to disclose a dashpot having a cylindrical housing, a piston separating front and rear cylinder chambers, a piston rod, and a connecting member affixed to the rod and another member affixed to the housing. A main control valve is provided with helical grooves to ensure that if the main control valve if blocked pressure compensation will occur between the front and rear cylinder chambers.
In 1992, U.S. Pat. No. 5,102,109 issued to Schnetz for a “Hydraulic Shock Absorber” and purports to disclose a shock absorber having a pressure dependent damping and piston stroke dependent damping so as to provide damping independent of the type and intensity of the motion to be damped. The shock absorber includes a piston dividing a high-pressure space from a low-pressure space, a piston rod and a compensatory piston. A relief valve handles damping caused by an increase in pressure. The relief valve includes transfer ducts and spring washers that react to the pressure to close the ducts gradually. This arrangement is useful for small energy, low speed impacts. Damping based the piston stroke is handled by a port through the piston and a stationary pin that progressively plugs the port as the piston moves toward the pin. This arrangement is useful with high energy, high-speed impacts.
In 2005, U.S. Pat. No. 6,863,163, for a “Self Leveling Vehicle Suspension Damper” issued to Oliver, Kruckemeyer, Bishop and Jensen, and purports to disclose a suspension damper capable of adjusting the height of a support vehicle while being concealed within the damper. The damper includes a reservoir tube forming an outer housing and an internal tube with a pressurized gas chamber, and a fluid chamber separated by a slidable gas piston. In the fluid chamber is a fluid piston and rod. The internal tube forms the usual fluid pumping chamber. Between the outer housing and the internal tube is a fluid reservoir. For adjusting height of the connected vehicle the internal tube has a number of holes and in the fluid reservoir between the housing and the internal tube is a moving first partition and a control second partition and a chamber between them. When the piston and rod are moving during a compression stroke pressure differences are created between the holes in the internal tube. This pressure is directed to the second partition and causes fluid to be added in the chamber between the partitions causing the first partition to move the first partition thereby reducing the volume available to pressurized gas. The lower volume increases gas pressure and exerts a on the rod so as to increase the height of the connected vehicle.